This invention relates to a method for the treatment of flue dusts containing arsenic and/or antimony from pyrometallurgical methods, wherein a reducing agent is added to the flue dusts, the flue dusts are heated together with the reducing agent, and volatile components are separated. This invention further-more comprises an apparatus for carrying out the method according to the invention.
Copper (Cu), nickel (Ni), zinc (Zn) or similar nonferrous metals are obtained from sulfidic ores. These metals as such represent valuable products which can be processed further in a variety of ways, but must be present in very pure form for this further treatment. This purity is generated by means of pyrometallurgical methods. Pyrometallurgy is understood to be the further thermal treatment of ores or metals obtained already, either by an oxidizing method, i.e. heating with the addition of oxygen, or by a reducing method, i.e. heating in a furnace atmosphere free from oxygen.
Using the example of the smelting of copper ores, a typical pyrometallurgical method will now briefly be described: Concentrates in the form of sulfidic flotation products typically are used as starting substance. These flotation products typically contain copper for about one third, iron for another third, and sulfur for the remaining third. In low concentrations, a plurality of further elements also are contained, above all arsenic (As), antimony (Sb), bismuth (Bi), cadmium (Cd) and lead (Pb). While carrying out the pyrometallurgical method, three phases are obtained, namely the matte, slag and waste gas phases. The waste gas phase not only contains gaseous compounds, but also flue dusts. The distribution of the impurities in the individual phases is obtained by the equilibrium reactions taking place.
The slag phase is obtained in that in a first processing step a part of the iron is separated from the copper concentrate by selective oxidation. At temperatures distinctly above 1000° C., the oxidized iron then is set in the liquid slag phase by adding sand.
The valuable product copper accumulates in the matte phase and in part also above the same in a separate copper slag phase.
Due to the high temperature, impurities, above all arsenic and antimony, are discharged in gaseous form. The waste gas thus loaded with heavy metals subsequently must at least partly be liberated from these impurities in a waste heat boiler and an electric gas cleaning. In the process, particles are formed by re-condensation. Together with entrained particles likewise contained in the waste gas, they form the so-called flue dusts.
Beside the impurities mentioned already, these flue dusts also contain comparatively high amounts of copper (20-30% w/w). For an increase in the process efficiency, the flue dusts themselves must therefore also be supplied to a smelting process, in order to separate the valuable product copper. At the same time, this smelting process must be carried out such that an enrichment of the impurities in the process is avoided.
Such reprocessing of flue dusts is described in DE 10 2010 011 242 A1, according to which these dusts containing arsenic and/or antimony are treated at temperatures between 500 and 1000° C. under an inert atmosphere and by adding sulfur, and a solid phase thus is separated from a gas phase. This gas phase then can be subjected to a further cleaning.
The described method relates to the recirculation of untreated flue dust to the smelter. However, in particular it is difficult to carry out with comparatively high contents of arsenic and/or antimony (2-10% w/w), since the chemical reactions taking place there are equilibrium reactions and thus parts of the contained arsenic and antimony get into the slag. A high content of arsenic and/or antimony in the slag, however, leads to the fact that this slag no longer can be disposed of easily or can even be used as valuable product for road construction, but rather must be disposed of as hazardous waste. If the recirculated flue dust contains 2-10% w/w of arsenic, the impurity collects in the slag phase of the smelter, which creates the described difficulty in slag disposal or slag usage.